The present invention relates generally to sensing of bearing loads and predicting of bearing life for anti-friction bearings, and more particularly to sensing of individual loads for a plurality of rolling elements in anti-friction bearings to characterize the load zone and predict useful life.
In its simplest form, a bearing includes a shaft or "journal" which is configured and arranged to be rotatably received within a mating hole of a structure. Anti-friction bearings or "rolling element bearings" are a type of bearing in which a plurality of rolling elements are disposed between the journal and mating hole to reduce friction.
The rolling elements of anti-friction bearings may take many forms, but are principally classified as balls or rollers. The rollers may likewise take a variety of forms, which are principally uniform cylinders, barrels or cones, depending upon the application.
A unique feature of rolling element bearings is that their useful life is not determined by wear, but rather by fatigue of the operating surfaces due to repeated stresses associated with use. It is generally accepted that fatigue failure of rolling element bearings occurs as a result of progressive flaking or pitting of the surfaces of the rolling elements and the surfaces of corresponding bearing races. This flaking and/or pitting causes the rolling elements to seize, thereby generating intense heat, pressure and friction.
Heretofore, efforts to predict useful life of rolling element bearings have centered around testing of the bearing as a whole. For example, to predict bearing life, a number of similar bearings are conventionally tested to failure while applying respectively varying rotational speeds and applied pressures. Conventional theories for predicting useful life of rolling element bearings have thereby sought to correlate measurable external factors of the bearing, such as applied load, temperature, and rotational speed, etc., with experimentally determined bearing failure points.
A number of conventional force measuring devices have been used to determine total applied force to a bearing. Lechler et al. set forth in U.S. Pat. No. 4,341,122 that the radial component of total applied force to a rolling element bearing may be measured through the use of strain gauges. According to Lechler et al., multiple strain gauges are used to compensate for changes in temperature during the calculation of total radial load. Likewise, Fujita et al. set forth in U.S. Pat. No. 5,140,849 that first and second strain gauges may be arranged in a perpendicular relation with respective output signals connected in a bridge circuit. According to Fujita et al., one of the strain gauges is used to measure strain while a perpendicular strain gauge provides for temperature compensation through electrical connection in the bridge circuit. Conventional force measuring devices for bearings have focused on the bearing as a whole. As a consequence, conventional force measuring devices have failed to accurately model forces which are dynamically exerted upon respective bearing rolling elements during rotation.
Conventional force measuring devices also suffer from a disadvantage in that a load zone of a bearing may not be accurately characterized during operation.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.